Liquid to liquid heat exchanger for a marine engine cooling system

ABSTRACT

A liquid to liquid heat exchanger for a marine engine cooling system disposes a tube bundle within a non-metallic shell, provides a thermostat within an integral portion of the shell, uses bolts that both push and pull respective end caps when rotated, and in one embodiment provides an integral deaeration reservoir to remove entrained gases from a liquid of a closed cooling system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to a heat exchanger and, more particularly, to a heat exchanger for a marine engine in which heat is exchanged between a coolant flowing within a closed cooling system and water drawn from a body of water and subsequently returned to that body of water after passing through the heat exchanger.

2. Description of the Related Art

Many types of heat exchangers are known to those skilled in the art for use in marine engine cooling systems. Although some marine engine cooling systems are open loop systems which circulate water, drawn from a body of water in which a marine vessel is operating, through all cooling passages of the propulsion system, other systems incorporate partially closed loop systems which circulate a coolant, such as ethylene glycol, through certain cooling passages of an engine and use water drawn from the body of water to remove heat from the coolant of the closed portion of the system. Those partially closed cooling systems typically incorporate liquid to liquid heat exchangers.

U.S. Pat. No. 4,360,350, which issued to Grover on Nov. 23, 1982, describes a hollow keel heat exchanger for marine vessels. The marine vessel has a hull with a hollow keel, generally of a non-metallic material, and an engine cooled by a closed loop, fresh water circulating cooling system. The keel is formed as a hollow keel chamber which has entry and exit apertures for circulating sea water through the chamber. A portion of the fresh water cooling system passes through the hollow keel chamber in heat exchange relation to the sea water providing a simple and efficient heat exchanger for cooling the engine.

U.S. Pat. No. 4,520,868, which issued to Grawey on Jun. 4, 1985, describes a heat exchanger. It has a plurality of longitudinally extending tubes disposed within a shell and includes an elastomeric end plate and means for compressing the elastomeric end plate and expanding the plate in the longitudinal direction and internal vibration-damping baffle plates. It avoids the problems of the prior art by providing an end wall assembly for a heat exchanger wherein an elastomeric end plate is mounted under compression in only a direction transversed to the tubes passing through the plate. The elastomeric end plate is not restrained in a longitudinal direction with respect to the tubes and as a result of the transversely applied compression force, the end plate is expanded in the longitudinal direction.

U.S. Pat. No. 4,643,249, which issued to Grawey on Feb. 17, 1987, describes a heat exchanger baffle plate. The baffle plate has a plurality of openings for receiving a plurality of longitudinally extending tubes and is disposed within a shell and is constructed of a vibration damping material.

U.S. Pat. No. 4,674,293, which issued to Clarke et al. on Jun. 23, 1987, describes a marine air conditioning heat exchanger. The heat exchanger is intended for use in a marine air conditioning system and is configured to provide the maximum possible heat transfer surface for the air being conditioned. The refrigerant coils and associated fins form the heat exchanger banks as usual, but instead of a single vertical bank, two banks are positioned at an angle to each other.

U.S. Pat. No. 5,004,042, which issued to McMorries et al. on Apr. 2, 1991, discloses a closed loop cooling system for a marine engine. A marine power system has closed loop cooling and includes a marine engine having a cooling fluid passage defined therethrough through which a cooling fluid stream may pass. A shell and tube heat exchanger has a tube side flow path and a shell side flow path defined therein. Cooling fluid conduits connect the cooling fluid passage from the marine engine to the tube side flow path so that the cooling fluid stream from the engine is directed through the tube side flow path of the heat exchanger. A raw water supply system directs a raw water stream from a body of water through the shell side flow path and then back to the body of water. The heat exchanger includes an outer housing and a tube bundle receiver in the outer housing. The outer housing is comprised of a shell and first and second end caps. The tube bundle includes a plurality of straight parallel tubes held between two spaced bundle bases. The housing and the bundle bases are constructed of non-metallic corrosion resistant materials. The tubes are constructed of metallic materials suitable for efficient heat transfer. The tubes are arranged in a plurality of substantially similar groups, each group being located in one of a plurality of cross-sectional areas.

The patents described above are hereby expressly incorporated by reference in the description of the present invention.

SUMMARY OF THE INVENTION

A liquid to liquid heat exchanger for a marine engine cooling system, made in accordance with a preferred embodiment of the present invention, comprises a non-metallic shell comprising first and second end caps which are attached to a cylindrical portion of the non-metallic shell, a tube bundle disposed within the non-metallic shell, wherein the tube bundle comprises a plurality of tubes. The internal cavities of the plurality of tubes are connected in fluid communication with each other to define a first path for a first liquid. The non-metallic shell and the tube bundle are configured to cooperate with each other to define a second path for a second liquid which directs the second liquid to flow in thermal contact with outer surfaces of the plurality of tubes and which causes the first and second liquids to be disposed in thermal communication with each other.

One embodiment of the present invention further comprises a first bolt which extends through a portion of the first end cap and is attached in threaded engagement with the tube bundle. The first bolt is configured to urge the first end cap toward the cylindrical portion of the non-metallic shell when the first bolt is rotated into the threaded engagement with the tube bundle and to urge the first end cap away from the cylindrical portion of the non-metallic shell when the first bolt is rotated out of threaded engagement with the tube bundle.

In a preferred embodiment of the present invention, the second path is connectable in fluid communication with an internal cooling jacket of the marine engine. The second liquid can comprise an ethylene glycol mixture. The first path in a preferred embodiment of the present invention is connectable in fluid communication with a pump for drawing water from a body of water in which the marine engine is operated.

In a preferred embodiment of the present invention, it further comprises a second bolt which extends through a portion of the second end cap and is attached in threaded engagement with a tube bundle. The second bolt is configured to urge the second end cap toward the cylindrical portion of the non-metallic shell when the second bolt is rotated into threaded engagement with the tube bundle and to urge the second end cap away from the cylindrical portion of the non-metallic shell when the second bolt is rotated out of threaded engagement with the tube bundle.

In a particularly preferred embodiment of the present invention, the first and second bolts are configured to fail in torsional shear upon an application of a predetermined magnitude of torque to a head of either bolt. The first and second bolts are rotatably attached to the first and second end caps, respectively, in a preferred embodiment of the present invention. The bolts are free to rotate relative to their associated end cap but are restricted from moving axially, in a direction parallel to the centerline of the bolts, relative to their associated end caps.

In a particularly preferred embodiment of the present invention, a thermostat is disposed in thermal communication with the second liquid and in serial association with the second path. A thermostat is disposed within a thermostat housing which is attached to the non-metallic shell. The thermostat housing is attached to a conduit which is formed as an integral portion of the non-metallic shell. A first flange is formed as an integral part of the conduit and shaped to be attached to a second flange which is formed as an integral part of the thermostat housing.

In one preferred embodiment of the present invention, a deaeration reservoir is formed as an integral part of the non-metallic shell. The deaeration reservoir is connected in fluid communication with the second path in order to direct a portion of the second liquid through the deaeration reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully and completely understood from a reading of the description of the preferred embodiment in conjunction with the drawings, in which:

FIG. 1 is an exploded isometric view of a heat exchanger made in accordance with one embodiment of the present invention;

FIG. 2 is an assembled isometric view of the heat exchanger shown in FIG. 1;

FIG. 3 is an isometric view of a tube bundle contained within the heat exchanger of the present invention;

FIG. 4 is a section view of the tube bundle of FIG. 3;

FIG. 5 is a section view of a bolt used in conjunction with a preferred embodiment of the present invention;

FIGS. 6 and 7 are isometric exploded views of end caps of a preferred embodiment of the present invention;

FIG. 8 is an isometric view of an embodiment of the present invention that incorporates an integral deaeration reservoir;

FIG. 9 is a section view of the embodiment illustrated in FIG. 8; and

FIG. 10 is a section view taken through a heat exchanger made in accordance with a preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Throughout the description of the preferred embodiment of the present invention, like components will be identified by like reference numerals.

FIG. 1 is an exploded isometric view of a liquid to liquid heat exchanger made in accordance with one preferred embodiment of the present invention. A non-metallic shell 10 comprises first and second end caps, 11 and 12, which are attached to a cylindrical portion 14 of the non-metallic shell. In a preferred embodiment, both end caps are also non-metallic. A tube bundle 20, which will be described in greater detail below, is disposed within the non-metallic shell 10. The tube bundle 20 comprises a plurality of tubes.

With continued reference to FIG. 1, a coolant inlet 26 and coolant outlet 28 are provided. A water inlet 30 and a water outlet 32 are provided to introduce a flow of water, from a body of water in which a marine engine is operated, through the internal cavities of the plurality of tubes contained within the tube bundle 20. The coolant inlet 26 is connected in fluid communication with the volume surrounding the plurality of tubes 20 within the non-metallic shell 10. This coolant, which can comprise ethylene glycol, is then eventually directed to the coolant outlet 28.

FIG. 2 is an isometric view of the heat exchanger with the individual components assembled. FIG. 3 shows the tube bundle 20 and FIG. 4 is a section view taken along a plane that intersects a central axis of the tube bundle 20.

With continued reference to FIGS. 1-4, the tube bundle 20 is disposed within the non-metallic shell 10. The tube bundle 20 comprises a plurality of tubes 38 that are held in position by their insertion through holes that extend through the thickness of a plurality of baffles 40. The tubes 38 also extend through holes formed in through the thickness of elastomeric tube sheets 42 located at the axial ends of the tube bundle 20.

With continued reference to FIGS. 1-4, a brass rod 46 extends along a central axis of the tube bundle 20. This brass rod is threaded at both ends to accept bolts which will be described in greater detail below. The internal cavities of the plurality of tubes 38 define a first path for a first liquid, such as water drawn from a lake or ocean in which the marine engine is being operated. The non-metallic shell 10 and the tube bundle 20 are configured to cooperate with each other to define a second path for a second liquid, such as a coolant comprising an ethylene glycol mixture, which directs the second liquid to flow in thermal contact with outside surfaces of the plurality of tubes 38. This causes the first and second liquids to be disposed in thermal communication with each other through the thickness of the walls of the plurality of tubes 38. The arrows in FIG. 4 indicate the second path of the second liquid.

With continued reference to FIGS. 1-4, the first and second end caps, 11 and 12, are attached to the tube bundle 20 by bolts which are identified by reference numeral 50 in FIG. 1. FIG. 5 is a section view of a bolt 50. FIGS. 6 and 7 are isometric views of the first 11 and second 12 end caps, respectively.

With reference to FIGS. 5-7, the bolts 50 are threaded at a distal end 54 and have a head 56 formed at the opposite end to facilitate the threading of the bolt 50 into and out of the threaded ends of the brass rod 46 which are identified by reference numeral 58 in FIG. 4. The bolts 50 are provided with two grooves, 61 and 62 which are shaped to receive O-rings, 71 and 72, respectively. It should be noted that groove 61 is deeper than groove 62. This greater depth of groove 61 is intentionally provided so that the bolt 50 will fail due to torsional shear at a predetermined magnitude of torque. That predetermined magnitude is selected to assure that the bolt will fail in the region of groove 61 prior to the threads 58 of the brass rod 46. It should be understood that the regions proximate the interface between the threads on the distal end 54 of the bolts 50 and the threads 58 within the brass rod 46 are located in a region that is exposed to water drawn from a body of water. This can lead to corrosion at the interface of the threads, particularly when the heat exchanger is used in a saltwater environment The screw failing in this manner results in a less expensive repair as compared to an internal thread failure in the brass rod.

With continued reference to FIGS. 5-7, a third groove 63 is shaped to receive a snap ring 76 which retains the bolt 50 in the axial position defined by the flange 78 on the bolt 50, the snap ring 76 and the hole extending through the end caps, 11 and 12, through which the bolts 50 are disposed. The configuration of the bolts 50, in cooperation with the snap ring 76, performs a significantly advantageous function. The bolts are configured to urge the associated end cap, 11 or 12, toward the cylindrical portion 14 of the non-metallic shell 10 when the bolt is rotated into the threaded engagement with the threads 58 of the brass rod 46 shown in FIG. 4. This configuration also urges the associated end cap, 11 or 12, away from the cylindrical portion 14 of the non-metallic shell 10 when the bolt is rotated out of its threaded engagement with the threads 58 in the brass rod 46 of the tube bundle 20. As a result, this configuration of the bolt and snap ring 76 assist the removal and replacement of the associated end cap whether the end cap is being removed from the heat exchanger or attached to the heat exchanger. The flange 78 of the bolt 50 and the snap ring 76 in groove 63 can provide either a push force and a pull force on the associated end cap, 11 or 12, to provide a significant benefit during the removal and reattachment of the end caps.

With continued reference to FIG. 1, a thermostat 80 is disposed in thermal communication with the second liquid and in serial association with the second path. The thermostat 80 is disposed within a thermostat housing 82 that is attached to the non-metallic shell 10. The thermostat housing 82 is attached to a conduit 84 that is formed as an integral portion of the non-metallic shell 10 in a particularly preferred embodiment of the present invention. A first flange 91 is formed as an integral part of the conduit 84 and shaped to be attached to a second flange 92 which is formed as an integral part of the thermostat housing 82. The thermostat housing 82 can be bolted to the conduit 84 as shown in FIG. 2. Flanges 91 and 92 are asymmetrical. This facilitates assembly and assures that hose connection 26 is always correctly oriented. Elastomeric seal 81, installed over the flange of thermostat 80, seals the thermostat housing to the mating flange interface.

For convenience in evacuating the air from the second fluid circuit during the filling process, an opening 96 is provided at the top portion of the cylindrical shell. A plug 97 is provided to close the opening. A bypass conduit 99, shown in FIG. 9, is provided to recirculate the coolant that does not flow past the thermostat 80 and through the conduit 84.

FIGS. 8 and 9 show isometric and section views of an alternative embodiment of the present invention. A deaeration reservoir 100 is formed as an integral part of the non-metallic shell 10 and, more particularly, as an integral part of the cylindrical portion 14 of the non-metallic shell. The second liquid can flow into the cavity defined by the deaeration reservoir 100 through an orifice 104 shown in FIG. 9 and extending through a wall of the cylindrical portion 14 of the non-metallic shell 10 and also through an inlet which is identified by reference numeral 106 in FIG. 8. The second liquid can flow out of the deaeration reservoir 100 through conduit 110 shown in FIG. 8. The inlets and outlet of the deaeration reservoir 100 are sized to assure a relatively slow flow of the second liquid through the reservoir 100 in parallel to the flow of the second liquid through the heat exchanging part of the structure. This reduced velocity of flow allows gases to escape from the second liquid and remain in the upper portion of the deaeration reservoir 100. The cap 110 is configured to allow gases to escape from the cavity 112 within the deaeration reservoir 100 when pressure exceeds a preselected magnitude. Through this method, the gases are removed from the second liquid.

FIG. 10 is a section view of one end of the heat exchanger. It shows a bolt 50 threaded into a threaded end 58 of the brass rod 46 with the O-rings (identified in FIGS. 6 and 7 by reference numerals 71 and 72). The combination of the flange 78 and snap ring 76 provide mechanical advantage when the end cap is being attached to the tube bundle 20 or removed therefrom. This operation is the same for the bolts 50 used in conjunction with both end caps, 11 and 12.

With reference to FIGS. 1, 6 and 7, it should be understood that the first liquid flows through the inside portions of the tubes in a multi-pass manner. In other words, water entering the raw water inlet 30 flows through a first compartment 111 and is directed through a first group of tubes whose ends are disposed proximate the first compartment 111. The first liquid then flows, from left to right in FIG. 1, toward the second end cap 12. The first liquid then flows into the compartment 112 of the second end cap 12 and is turned back toward the left in FIG. 1. After the first liquid travels from right to left in FIG. 1 and into the third cavity 113 of the first end cap 11, it is again reversed so that it flows back toward the second end cap 12 from the cavity identified by reference numeral 114. Eventually, the first liquid is again reversed at cavity 115 to flow again toward the right and toward the second end cap 12 where it flows into the cavity identified by reference numeral 116. From there, it flows out of the outlet 32 to be returned to the body of water from which it was originally drawn.

With reference to FIGS. 1 and 4, the exchange of heat occurs with calories flowing from the second liquid, which flows along a second path represented by the arrows in FIG. 4, to the first liquid which flows in the manner described above in conjunction with FIGS. 1, 6 and 7. In FIGS. 6 and 7, O-rings 120 provide a seal between the end caps, 11 and 12, and the cylindrical portion 14 of the non-metallic shell 10.

With reference to FIGS. 1-10, it can be seen that a liquid to liquid heat exchanger for a marine engine cooling system made in accordance with a preferred embodiment of the present invention comprises a non-metallic shell 10 which comprises first and second end caps, 11 and 12, which are attached to a cylindrical portion 14. A tube bundle 20 is disposed within the non-metallic shell 10. The tube bundle comprises a plurality of tubes 38. The internal cavities of the plurality of tubes 38 are connected in fluid communication with each other to define a first path for a first liquid, such as water drawn from a body of water. The non-metallic shell 10 and the tube bundle 20 are configured to cooperate with each other to define a second path, which is illustrated by arrows in FIG. 4, for a second liquid, such as an ethylene glycol mixture, which directs the second liquid to flow in thermal contact with outside surfaces of the plurality of tubes 38 and which causes the first and second liquids to be disposed in thermal communication with each other. First and second bolts 50 extend through portions of the first and second end caps, 11 and 12, and are attached in threaded engagement with a brass rod 46 of the tube bundle 20. The bolts are configured to urge the associated end caps toward the cylindrical portion 14 when they are rotated into threaded engagement with the tube bundle 20 and to urge the associated end cap away from the cylindrical portion 14 when they are rotated out of threaded engagement with the brass rod 46 of the tube bundle 20. The second path of the second liquid is connectable in fluid communication with an internal cooling jacket of the marine engine and the second liquid, in a particularly preferred embodiment of the present invention, can comprise an ethylene glycol mixture. The first path, of the water drawn from the body of water, is connectable in fluid communication with a pump for drawing water from the body of water in which the marine engine is operated. The connections between the heat exchanger and the engine and water pump are very well known to those skilled in the art and will not be further described herein. The bolts 50 are configured to fail in torsional shear upon an application of a predetermined magnitude of torque to a head 56 of the bolt 50. This failure is caused to occur at the first slot 61 which is formed deeper than other slots of the bolt 50. The bolts 50 are rotatably attached to the first and second end caps, 11 and 12, respectively and are limited in their axial movement relative to their associated end cap. A thermostat 80 is disposed in thermal communication with the second liquid and in serial association with the second path. The thermostat is disposed within a thermostat housing 82 which is attached to the non-metallic shell 10. The thermostat housing 82 is attached to a conduit 84 which is formed as an integral portion of the non-metallic shell 10. A first flange 91 is formed as an integral part of the conduit 84 and shaped to be attached to a second flange 92 which is formed as an integral part of the thermostat housing 82. In one embodiment of the present invention, a deaeration reservoir 100 is formed as an integral part of the non-metallic shell 10 and, more particularly, as an integral part of the cylindrical portion 14 of the non-metallic shell. The deaeration reservoir 100 is connected in fluid communication with the second path, which is illustrated by arrows in FIG. 4, to direct a portion of the second liquid through the deaeration reservoir 100.

Although the present invention has been described with particular specificity and illustrated to show a plurality of embodiments, it should be understood that alternative embodiments are also within its scope. 

1. A liquid to liquid heat exchanger for a marine engine cooling system, comprising: a nonmetallic shell comprising first and second end caps which are attached to a cylindrical portion of said nonmetallic shell; a tube bundle disposed within said nonmetallic shell, said tube bundle comprising a plurality of tubes, the internal cavities of said plurality of tubes being connected in fluid communication with each other to define a first path for a first liquid, said nonmetallic shell and said tube bundle being configured to cooperate with each other to define a second path for a second liquid which directs said second liquid to flow in thermal contact with outside surfaces of said plurality of tubes and which causes said first and second liquids to be disposed in thermal communication with each other; a first bolt which extends through a portion of said first end cap and is attached in threaded engagement with said tube bundle, said first bolt being configured to urge said first end cap toward said cylindrical portion when said first bolt is rotated into said threaded engagement with said tube bundle and to urge said first end cap away from said cylindrical portion when said first bolt is rotated out of said threaded engagement with said tube bundle, said first bolt being configured to fail in torsional shear at a preselected location upon an application of a predetermined magnitude of torque to a head of said bolt, said preselected location being axially displaced from said tube bundle; and wherein said bolt has a groove therein at said preselected location, and axially spaced from the location of said threaded engagement.
 2. The heat exchanger of claim 1, wherein: said groove is a failure groove; said bolt has one or more other sealing grooves therein each receiving a respective O-ring; and said failure groove has a greater depth than each of said one or more sealing grooves.
 3. The heat exchanger of claim 2, wherein: said one or more sealing grooves are axially spaced between said failure groove and said location of said threaded engagement, such that said failure groove is on one axial side of said one or more sealing grooves, and said location of said threaded engagement is on the other distally opposite axial side of said one or more sealing grooves, such that upon torsional shear failure at said failure groove at said preselected location, the sealing at said one or more sealing grooves and their respective O-rings remains intact.
 4. The heat exchanger of claim 2, wherein: said first path is connectable in fluid communication with a pump for drawing water from a body of water in which said marine engine is operated.
 5. The heat exchanger of claim 1, further comprising: a second bolt which extends through a portion of said second end cap and is attached in threaded engagement with said tube bundle, said second bolt being configured to urge said second end cap toward said cylindrical portion when said second bolt is rotated into said threaded engagement with said tube bundle and to urge said second end cap away from said cylindrical portion when said second bolt is rotated out of said threaded engagement with said tube bundle.
 6. (canceled)
 7. The heat exchanger of claim 5, wherein: said first and second bolts are rotatably attached to said first and second end caps, respectively.
 8. The heat exchanger of claim 1, further comprising: a thermostat disposed in thermal communication with said second liquid and in serial association with said second path, said thermostat being disposed within a thermostat housing which is attached to said nonmetallic shell. 9-20. (canceled)
 21. A liquid to liquid heat exchanger for a marine engine cooling system, comprising: a nonmetallic shell comprising first and second end caps which are attached to a cylindrical portion of said nonmetallic shell; a tube bundle disposed within said nonmetallic shell, said tube bundle comprising a plurality of tubes, the internal cavities of said plurality of tubes being connected in fluid communication with each other to define a first path for a first liquid, said first path being connectable in fluid communication with a pump for drawing water from a body of water in which said marine engine is operated, said nonmetallic shell and said tube bundle being configured to cooperate with each other to define a second path for a second liquid which directs said second liquid to flow in thermal contact with outside surfaces of said plurality of tubes and which causes said first and second liquids to be disposed in thermal communication with each other, said second path being connectable in fluid communication with an internal cooling jacket of said marine engine; a thermostat disposed in thermal communication with said second liquid and in serial association with said second path, said thermostat being disposed within a thermostat housing which is attached to said nonmetallic shell, said thermostat housing being attached to a conduit which is formed as an integral portion of said nonmetallic shell, a first flange being formed as an integral part of said conduit and shaped to be attached to a second flange which is formed as an integral part of said thermostat housing; a first bolt which extends through a portion of said first end cap and is attached in threaded engagement with said tube bundle, said first bolt being configured to urge said first end cap toward said cylindrical portion when said first bolt is rotated into said threaded engagement with said tube bundle and to urge said first end cap away from said cylindrical portion when said first bolt is rotated out of said threaded engagement with said tube bundle, said first bolt being configured to fail in torsional shear at a preselected location on said first bolt upon an application of a predetermined magnitude of torque to a head of said bolt, said preselected location being axially displaced from said tube bundle; a second bolt which extends through a portion of said second end cap and is attached in threaded engagement with said tube bundle, said second bolt being configured to urge said second end cap toward said cylindrical portion when said second bolt is rotated into said threaded engagement with said tube bundle and to urge said second end cap away from said cylindrical portion when said second bolt is rotated out of said threaded engagement with said tube bundle, said first and second bolts are rotatably attached to said first and second end caps, respectively; and wherein said bolt has a groove therein at said preselected location and axially spaced from the location of said threaded engagement, said groove is a failure groove, said bolt has one or more other sealing grooves therein each receiving a respective O-ring, said failure groove has a greater depth than each of said one or more sealing grooves, said one or more sealing grooves are axially spaced between said failure groove and said location of said threaded engagement, such that said failure groove is on one axial side of said one or more sealing grooves, and said location of said threaded engagement is on the other distally opposite axial side of said one or more sealing grooves, such that upon torsional shear failure at said failure groove at said preselected location, the sealing at said one or more sealing grooves and their respective O-rings remains intact.
 22. A liquid to liquid heat exchanger for a marine engine cooling system, comprising: a nonmetallic shell comprising first and second end caps which are attached to a cylindrical portion of said nonmetallic shell; a tube bundle disposed within said nonmetallic shell, said tube bundle comprising a plurality of tubes, the internal cavities of said plurality of tubes being connected in fluid communication with each other to define a first path for a first liquid, said first path being connectable in fluid communication with a pump for drawing water from a body of water in which said marine engine is operated, said nonmetallic shell and said tube bundle being configured to cooperate with each other to define a second path for a second liquid which directs said second liquid to flow in thermal contact with outside surfaces of said plurality of tubes and which causes said first and second liquids to be disposed in thermal communication with each other; a deaeration reservoir formed as an integral part of said nonmetallic shell, said deaeration reservoir being connected in fluid communication with said second path to direct a portion of said second liquid through said deaeration reservoir; a thermostat disposed in thermal communication with said second liquid and in serial association with said second path, said thermostat being disposed within a thermostat housing which is attached to said nonmetallic shell, said second path is connectable in fluid communication with an internal cooling jacket of said marine engine, said second liquid comprising ethylene glycol; a first bolt which extends through a portion of said first end cap and is attached in threaded engagement with said tube bundle, said first bolt being configured to urge said first end cap toward said cylindrical portion when said first bolt is rotated into said threaded engagement with said tube bundle and to urge said first end cap away from said cylindrical portion when said first bolt is rotated out of said threaded engagement with said tube bundle, said first bolt being configured to fail in torsional shear at a preselected location on said first bolt upon an application of a predetermined magnitude of torque to a head of said bolt, said preselected location being axially displaced from said tube bundle; a second bolt which extends through a portion of said second end cap and is attached in threaded engagement with said tube bundle, said second bolt being configured to urge said second end cap toward said cylindrical portion when said second bolt is rotated into said threaded engagement with said tube bundle and to urge said second end cap away from said cylindrical portion when said second bolt is rotated out of said threaded engagement with said tube bundle, said first and second bolts being rotatably attached to said first and second end caps, respectively; a first bolt which extends through a portion of said first end cap and is attached in threaded engagement with said tube bundle, said first bolt being configured to urge said first end cap toward said cylindrical portion when said first bolt is rotated into said threaded engagement with said tube bundle and to urge said first end cap away from said cylindrical portion when said first bolt is rotated out of said threaded engagement with said tube bundle; a second bolt which extends through a portion of said second end cap and is attached in threaded engagement with said tube bundle, said second bolt being configured to urge said second end cap toward said cylindrical portion when said second bolt is rotated into said threaded engagement with said tube bundle and to urge said second end cap away from said cylindrical portion when said second bolt is rotated out of said threaded engagement with said tube bundle, said first and second bolts being rotatably attached to said first and second end caps, respectively; and at least one of said bolts has a groove therein at said preselected location and axially spaced from the location of said threaded engagement, said groove is a failure groove, said one bolt has one or more other sealing grooves therein each receiving a respective O-ring, said failure groove has a greater depth than each of said one or more sealing grooves, said one or more sealing grooves are axially spaced between said failure groove and said location of said threaded engagement, such that said failure groove is on one axial side of said one or more sealing grooves, and said location of said threaded engagement is on the other distally opposite axial side of said one or more sealing grooves, such that upon torsional shear failure at said failure groove at said preselected location, the sealing at said one or more sealing grooves and their respective O-rings remains intact. 